The imperfect tooth of the species called by Dr. Harlan _Megalonyx laqueatus_, and of which a cast was presented by that able and industrious naturalist to the Museum of the Royal College of Surgeons, resembles in general form, and especially in the characteristic double longitudinal groove on the inner side, the tooth of the _Megalonyx Jeffersonii_. It is thus described by Dr. Harlan: “The fractured molar tooth appears to have belonged to the inferior maxilla on the right side; the crown is destroyed; a part of the cavity of the root remains. The body is compressed transversely, and presents a double curvature, which renders its anterior and exterior aspects slightly convex; the posterior and interior gently concave; these surfaces are all uniform, with the exception of the interior or mesial aspect, which presents a longitudinal rib or ridge, one-half the thickness of the long diameter of the tooth; with a broad, not profound longitudinal groove or channel along each of its borders. It is from this resemblance to a portion of a fluted column, that the animal takes its specific appellation (_Meg^x. laqueatus_). “The crown would resemble an irregular ellipsis widest at the anterior portion. The tooth consists of a central pillar of bone surrounded with enamel, the former of a dead white, the latter of a ferruginous brown colour: the transverse diameter is more than two-thirds less than its length, whilst that of _Meg^x. Jeffersonii_ is only one-third less—the antero-posterior diameter is one-half its length in the former, and two-thirds less in the latter. The proportions of this tooth are consequently totally at variance with that of its kindred species.” [Vide Pl. XII. fig. 7, 8, 9.][36] Dr. Harlan describes also two claws of the fore-foot, a radius, humerus, scapula, one rib, an os calcis, a metacarpal bone, certain vertebræ, a femur, and tibia, of the same _Megalonyx_; these parts of the skeleton, together with the tooth, which so fortunately served to establish the generic relationship of the species with the _Megalonyx_ of Jefferson and Cuvier, were discovered in Big-bone-cave, Tennessee, United States. Dr. Harlan does not enter into the question of the generic characters of _Megalonyx_, but it would seem that he felt them to rest not entirely on dental modifications, for he observes that “a minute examination of the tooth and knee-joint renders it not improbable, supposing the last named character to be peculiar to it, that if the whole frame should hereafter be discovered, it may even claim a generic distinction, in which case, either Aulaxodon, or PLEURODON, would not be an inappropriate name.”[37]